1. Field
This disclosure relates generally to power control and, more specifically, transmit power control techniques for nodes in an ad-hoc network.
2. Related Art
An ad-hoc network is a decentralized type of network that does not rely on a pre-existing infrastructure. In general, each node in a wireless ad-hoc network may forward data for other nodes. The decentralized nature of wireless ad-hoc networks makes ad-hoc networks suitable for a variety of applications, e.g., applications where a dedicated implementation of a fixed management node is not desirable. Implementation of dynamic and adaptive routing protocols enable ad-hoc networks to be formed relatively quickly. Wireless ad-hoc networks may take various forms, e.g., a mobile ad-hoc network (MANET), a wireless mesh network (WMN), and a wireless sensor network (WSN).
In general, a wireless ad-hoc network is made up of multiple nodes that are connected by wireless links. As wireless links can be established at any time, wireless ad-hoc networks are usually designed for dynamic restructuring in a manner that is timely, efficient, reliable, robust, and scalable. Typically, nodes of a wireless ad-hoc network compete for access to a shared frequency spectrum, which can result in collisions (interference) between communications of the nodes.
Carrier sense multiple access (CSMA) is a probabilistic media access control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as a band of the electromagnetic spectrum. Carrier sense means that each node attempts to detect the presence of an encoded signal (transmitted from another node) before attempting to transmit. If a carrier is sensed, a node waits for a transmission to finish before initiating its own transmission. Multiple access means that multiple nodes send and receive signals on the same channel. CSMA with collision detection (CSMA/CD) is a modification of CSMA that attempts to improve CSMA performance by terminating transmission as soon as a collision is detected, while reducing the probability of a second collision on a transmission retry. CSMA with collision avoidance (CSMA/CA) is another modification of CSMA. CSMA/CA attempts to improve the performance of CSMA by attempting to be less greedy on a channel. For example, in systems employing CSMA/CA, if a channel is sensed by a node as being busy before a transmission, the transmission is deferred for a random interval to reduce the probability of collisions on the channel.
The IEEE 802.15.4-2006 standard (which has been maintained by the IEEE 802.15 working group) specifies a physical layer and MAC layer for low-rate wireless personal area networks (PANs). The IEEE 802.15.4-2006 standard provides the basis for the ZigBee™, wireless highway addressable remote transducer (WirelessHART™), and MiWi™ specifications. Currently, the IEEE 802.15 working group is working on a number of next generation standards focused on applications in industrial, radio frequency identification (RFID), smart utility networks (SUN), critical infrastructure management, and body area networks.
The IEEE 802.15.4-2006 standard defines two types of network nodes, i.e., a full-function device (FFD) and a reduced-function device (RFD). An FFD can serve as a coordinator node of a network or as a common node. An FFD implements a general model of communication that allows the FFD to talk to any other device. An FFD may relay messages, in which case the FFD is designated as a coordinator node (or a network coordinator node when the FFD is in charge of the entire network). In general, RFDs are relatively simple devices with relatively low resource and communication requirements and, as such, usually only communicate with FFDs and never act as coordinator nodes. When a PAN takes the form of a peer-to-peer network, arbitrary patterns of connections may be achieved, limited only by the distance between each pair of nodes.
IEEE 802.15.4 g smart utility network (SUN) task group is operative under the umbrella of the IEEE 802.15 working group and is chartered to create a physical (PHY) amendment to IEEE 802.15.4 to provide a global standard that facilitates very-large scale process control applications, such as a smart-grid utility network capable of supporting large, geographically diverse networks with minimal infrastructure (with potentially millions of fixed endpoints).